Those of ordinary skill in the art will appreciate that living cells within a biological body are constantly undergoing metabolic activities. These biochemical and physical metabolic processes generate heat. Certain cells, like cancer cells, have been shown to have a high metabolic rate, thus producing a high amount of heat relative to other cells. On the other hand, bones have a lower metabolic rate and generate lower amount of heat. Aging or lifeless cells do not emit heat, but rather absorb heat.
Thermal radiation resulting from the metabolic generation of heat emanates from the human body. The patterns of such thermal emissions are affected by the activities of the tissues, organs and vessels inside the body. The amount of radiation can reflect the metabolic rate of the human body.
The application of clinical thermography, a technology involving the measurement and displaying of self-emanating radiation to reveal thermal changes on the surface of the human body, began possibly as early as the 1930's. Over the years, thermographic technology has been extensively tested and examined in clinical studies.
One example of a prior art thermographic scanning system is U.S. Pat. No. 3,909,521 to Hunt et al., entitled "Infrared Imaging System." Hunt et al. discloses a pair of mirror systems which scan an object in two dimensions over an infrared detector.
U.S. Pat. No. 3,862,423 to Kutas et al., entitled "Scanning Thermography," proposes a scanning assembly including a scanning mirror mounted for continuous rotational scanning about one axis and oscillatory scanning about an orthogonal axis. Kutas et al. discusses the applicability of such scanning systems to medical thermography applications.
In prior art scanning thermography systems, an infrared sensor is used to convert thermal radiation into electric signals. The thermal image can be generated by means of either an optical scanning system or a pyroelectric vidicon television tube. A video monitor or the like can be used to display the image. Computer imaging technology has been deemed desirable by physicians since it is non-invasive and may require no physical contact with the body. A great deal of research has been conducted on such technology in connection with the clinical diagnosis and examination of such conditions as arthritis and phlebothrombosis, and other diseases including, notably, mastrocarcinoma (breast cancer).
The theory underlying conventional thermographic techniques as applied to cancer is that the change of the pulse distribution around a cancerous area and the rate of metabolism are greater than the general tissue, resulting in a higher temperature at the skin surface. Presently known thermography technology may have limited sensitivity and specificity, however, resulting in a high percentage of false positive and false negative assessments. The medical community's enthusiasm for thermography technology in the 1970's appeared to subside in the 1980's. In the last 10 years, it is believed that very little advancement has been made in the field of thermography.
If only the temperature of the skin surface can be measured while the relationship between the surface temperature and the emissions from the inside of the body cannot be established, then application of thermal imaging technology is limited. It is believed, therefore, that it would be desirable to provide a method and apparatus for revealing the relationship between the skin's surface radiation temperature and internal thermal radiation sources. Through image processing and measurement technology, surface or internal radiation sources can be non-invasively distinguished through extrapolation. It is believed that such technology would prove to be clinically effective in the detection and diagnosis of cancers (especially in their early stages) and other diseases.
The temperature of a live human body is between 20.degree. C. and 40.degree. C. at room temperature (20.degree. C.). Differences in skin color do not significantly affect the body temperature or the emission of the thermal radiation. The wavelength of this thermal radiation is between 8 and 13 mm, which is often referred to as "infrared" region in the electromagnetic wave spectrum, the infrared region having a longer wavelength than the red or near-red spectrum. The physics of infrared radiation has been investigated extensively, and its application in thermal metabolism imaging is relatively well-known to those of ordinary skill in the art.
There are various biochemical and biophysical mechanisms that can produce heat in a live biological body. A biological body will absorb thermal energy if its temperature is below that of the environment, or will emit thermal energy if its temperature is above that of the environment. The latter condition is the preferred mode of detecting and imaging thermal metabolic activity.
Superficial (i.e., surface) thermal radiation from the skin of a biological body has previously been studied. The present invention, on the other hand, involves the thermal radiation associated with thermal conduction within the body.
There are multiple heat sources within a biological body. Although it is possible to calculate the thermal radiation from a thermal body by thermodynamics, the complexity of the boundary conditions associated with the biological body makes this approach impractical. Therefore, a practically viable method that can be used to solve the problem of imaging internal heat sources within a thermal body has not heretofore been shown. The present invention involves formulation of a new method and apparatus for analysis of a thermal system based on an analogy to electrical circuit theory; this method may be referred to herein as a "thermal-electric analogue" method.
Infrared radiation passes through a transparent medium, air, for example, at the speed of light. Thus, heat is transferred in air by thermal radiation. In a material body, on the other hand, heat transfer is based on thermal conduction resulting in establishment of thermal equilibrium. From the point of view of thermal radiation, infrared radiation deep within the body cannot be readily detected from outside. Therefore, there has not heretofore been shown a method and apparatus for resolving heat sources within the body; prior infrared imaging has been restricted to viewing objects on the surface of the body. However, in accordance with one aspect of the present invention, it is proposed that, based on the conduction of heat to establish thermal equilibrium, thermal sources lying within the body can be imaged. That is, based upon the thermal conditions at the surface of a patient's body, information about internal regions can be derived through extrapolation.
Thermal metabolism imaging systems used in clinical diagnosis are preferably not influenced by particular patient conditions or environmental conditions. Prior art thermograph machines have not been widely used because they generally do not satisfy this requirement. Accordingly, it is another aspect of the present invention that an imaging system is provided which is less sensitive disturbance from the patient and from the environment.